This .Net class wraps AcGeNurbCurve2d ObjectARX class. This class represents non-uniform rational B-spline in 2D space.

Autodesk.AutoCAD.Geometry.Entity2d
    Autodesk.AutoCAD.Geometry.Curve2d
        Autodesk.AutoCAD.Geometry.SplineEntity2d
            Autodesk.AutoCAD.Geometry.NurbCurve2d

Public sealed Class NurbCurve2d
Inherits SplineEntity2d

public sealed class NurbCurve2d : SplineEntity2d;